1 Field of the Invention
This invention relates to a ceramic composition having high sorptive capacity for oxygen at elevated temperature. Such ceramic composition may be employed for example in an elevated temperature pressure swing adsorption system for separation of oxygen-containing feed gas mixtures.
2. Description of the Related Art
In the field of gas separation for the production of industrial gases, a variety of technologies have been employed in the art, including: cryogenic separation processes involving cooling and pressurizing a feed gas mixture to form a liquid that then undergoes distillation; chemisorption or chemical reaction removal of unwanted gas species from a feed gas mixture to yield the desired gas component as the only remaining gas-phase product; scrubbing of the feed gas mixture to remove undesired soluble components therefrom, chromatographic separation of the feed gas mixture; and physical adsorption-based processes.
The latter approach of physical adsorption-based processes includes pressure swing adsorption (PSA) in which a bed of physical adsorbent material is contacted with a feed gas mixture including one or more components for which the physical adsorbent material has sorptive affinity, to preferentially adsorb such components, while the non-adsorbed components flow out of the contacting zone containing the adsorbent material. The adsorbent material then is lowered in pressure in relation to the pressure at which the feed gas mixture is contacted with the adsorbent material, e.g., by a xe2x80x9cblow-downxe2x80x9d or depressurization step, or alternatively by vacuum desorption, whereby the previously sorbed gas components desorb from the adsorbent material and are discharged from the adsorbent material.
The foregoing PSA process may be carried out in a multiplicity of adsorbent beds, joined together by valved manifolds at their respective inlet ends and at their outlet ends, and coupled at the inlet manifold to a source of the feed gas mixture to be separated. In operation, the valves are operated to carry out a cyclic, repetitive process in which at least one of the beds is undergoing active processing of gas mixture, while another or others are off-line or undergoing regeneration. Thus, a first bed of a multibed PSA system may be undergoing pressurization with feed gas mixture, while a second bed undergoes depressurization and discharge of previously sorbed gas therefrom. The regeneration may entail use of a purge or displacement gas, or use of embedded heat exchange coils to aid in desorbing gas from the bed.
A wide variety of sorbent materials have been used or proposed for use in PSA systems, including zeolites, activated carbon, silica, alumina, etc. The search for new sorbent materials forms a continuing focus of the gas products industry, particularly for the production of commodity industrial gases such as oxygen, nitrogen, argon, etc.
By way of specific example, systems for the commercial production of oxygen from air by PSA or vacuum-pressure swing adsorption (VPSA) frequently use zeolites as an adsorbent. Nitrogen is more strongly adsorbed than oxygen on zeolites, so when high pressure air is placed in contact with these materials, an oxygen-rich atmosphere is left. Lowering the pressure over the adsorbent bed allows the adsorbed nitrogen to reenter the gas phase (such desorbate then may be used as a nitrogen source), and the cycle is repeated. Using vacuum in the cycle (PVSA) results in slightly better performance.
PSA and VPSA techniques alone typically deliver oxygen with a purity of 90-95%, with nitrogen and argon as the major impurities. Where this purity level is acceptable, oxygen can be generated on-site.
Oxygen, however, frequently is desired to be produced at a purity level on the order of 99+%, and this is difficult to achieve economically in commercially available PSA and VPSA systems.
Polymeric membrane processes have been suggested as a potential solution to this problem, in view of the conceptually low capital costs, small size, light weight and simple operation of membrane-based separation systems. Nonetheless, efforts to produce oxygen economically with polymeric membranes have not been successful, as a result of poor permeation selectivity in commercially available polymeric membranes. In consequence, current polymeric membrane systems are not available to produce oxygen in high purity. Single-pass membrane units deliver 35-40% oxygen. Multiple pass units can go over 90%, but are not able to economically reach the aforementioned high purity threshold of 99+%.
The present invention provides a ceramic composition having high adsorptive affinity for oxygen at elevated temperature. Such ceramic composition may be usefully employed as an adsorbent medium in a PSA system to economically and efficiently sorptively remove oxygen from an oxygen-containing feed gas mixture, and produce extremely high purity product gas due to the selectivity of the ceramic composition for oxygen.
In one aspect, the invention relates to a ceramic composition having a high adsorptive capacity for oxygen at elevated temperature, comprising a ceramic material selected from the following group:
Bi2xe2x88x92yEryO3xe2x88x92d;
Bi2xe2x88x92yYyO3xe2x88x92d;
La1xe2x88x92yBayCo1xe2x88x92xNixO3xe2x88x92d;
La1xe2x88x92ySryCo1xe2x88x92xNixO3xe2x88x92d;
La1xe2x88x92yCayCo1xe2x88x92xNixO3xe2x88x92d;
La1xe2x88x92yBayCo1xe2x88x92xFexO3xe2x88x92d;
La1xe2x88x92ySryCo1xe2x88x92xFexO3xe2x88x92d; and
La1xe2x88x92yCayCo1xe2x88x92xFexO3xe2x88x92d;
wherein
x is from 0.2 to 0.8,
y is from 0 to 1.0 and
d=0.1 to 0.9.
Such ceramic composition may be in a divided form, e.g., beads, spheres, rings, toroidal shapes, irregular shapes, rods, cylinders, flakes, films, cubes, polygonal geometric shapes, sheets, fibers, coils, helices, meshes, sintered porous masses, granules, pellets, tablets, powders, particulates, extrudates, cloth or web form materials, honeycomb matrix monolith, composites with other components, or comminuted or crushed forms of the foregoing conformations.
The ceramic composition may additionally be coated on a substrate, such as a support in one of the conformations mentioned in the preceding paragraph.
The ceramic composition of the invention may be utilized in a divided form in a vessel, to provide a sorptive unit that may be employed in a process system for separation of oxygen from an oxygen-containing feed gas mixture that is flowed through the vessel for contacting with the ceramic composition.
In a further aspect, the invention relates to a ceramic composition having a high adsorptive capacity for oxygen at elevated temperature, in which the composition comprises a material selected from the group consisting of:
Bi1.55Er0.45O3xe2x88x92d;
Bi1.5Y0.5O3xe2x88x92d;
La0.6Sr0.4Co0.8Ni0.2O3xe2x88x92d;
La0.6Sr0.4Co0.6Ni0.4O3xe2x88x92d;
La0.6Sr0.4Co0.4Ni0.6O3xe2x88x92d;
La0.6Ba0.4Co0.8Fe0.2O3xe2x88x92d;
La0.6Sr0.4Co0.8Fe0.2O3xe2x88x92d; and
La0.6Ca0.4Co0.8Fe0.2O3xe2x88x92d;
wherein d=0 to 0.5.
In another aspect, the invention relates to a method of making a ceramic composition having a high adsorptive capacity for oxygen at elevated temperature, in which the composition comprises a material selected from the group consisting of:
Bi2xe2x88x92yEryO3xe2x88x92d;
Bi2xe2x88x92yYyO3xe2x88x92d;
La1xe2x88x92yBayCo1xe2x88x92xNixO3xe2x88x92d;
La1xe2x88x92ySryCo1xe2x88x92xNixO3xe2x88x92d;
La1xe2x88x92yCayCo1xe2x88x92xNixO3xe2x88x92d;
La1xe2x88x92yBayCo1xe2x88x92xFexO3xe2x88x92d;
La1xe2x88x92ySryCo1xe2x88x92xFexO3xe2x88x92d; and
La1xe2x88x92yCayCo1xe2x88x92xFexO3xe2x88x92d;
where
x is from 0.2 to 0.8,
y is from 0 to 1.0 and
d=0 to 0.9,
wherein the method comprises forming a mixture of respective oxalates of the corresponding metals in the ceramic composition, and calcining the mixture to form the ceramic composition as a crytalline oxide.
The mixture of respective oxalates of the corresponding metals in the ceramic composition is advantageously formed by combining the corresponding metals with oxalate ion, with the oxalate ion being formed by heating glycolic acid. The glycolic acid in turn may be produced by reaction of nitric acid and ethylene glycol.
In yet another aspect, the invention relates to a method of making a lanthanum calcium cobalt metal oxide, LaCaCoMO, wherein the metal M is selected from the group consisting of iron and nickel, comprising the steps of:
(a) reacting nitric acid and ethylene glycol to yield glycolic acid;
(b) heating the glycolic acid to form oxalate ion;
(c) reacting the oxalate ion with the metals La, Ca, Co and M to form a mixture of oxalates of said metals; and
(d) calcining the mixture of oxalates of the aforementioned metals to yield the lanthanum calcium cobalt metal oxide, LaCaCoMO.
As used herein, the term xe2x80x9chigh adsorptive capacityxe2x80x9d means an oxygen storage of at least 40 millimoles of oxygen per mole of the ceramic material when the ceramic material is contacted with oxygen gas at a temperature of 800xc2x0 C.
As used herein, the term xe2x80x9celevated temperaturexe2x80x9d means a temperature in the range of from 400xc2x0 C. to 1000xc2x0 C.
When metal oxide ceramics are referred to herein in symbolic notational form without stoichiometric subscripts (e.g., in the term LaCaCoMO), it is to be understood that the respective elemental constituents are present in such material in stoichiometrically appropriate proportions relative to one another.
Additional objects, features and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.